Level 2Project 2 · Session 30
30

Project 2 · Build 2 of 2

The output half, the join, and the stranger

What we are making: the finished machine, and then an honest look at it through somebody else's eyes.

First half: finish it

  1. Do not touch the input wiring. It works and you measured it.
  2. Wire the output. Test it on its own with a tiny program — no sensor involved.
  3. Only when both halves work separately, write the if that joins them.
  4. Test it ten times in a row. Count.

If it works twice in three tries

That is not working. It is marginal, and it will fail in front of visitors, because that is when marginal things fail. The cause is nearly always the threshold sitting too close to the normal reading — go back to your two numbers from session 29 and move it.

Second half: the stranger

  1. Swap with another team. Put your machine in front of them and say nothing.
  2. Write down every hesitation, every wrong move, every question.
  3. Swap back. Fix the three worst.
  4. Label it: what it is, what to do with it.
  5. Freeze. No code changes and no rewiring from the end of today.
💡 Tip
Explaining it is the one thing you will not be able to do at the exhibition, because you will be talking to somebody else at the time. Whatever you had to say out loud today is what the label or the screen has to say for you.
What you seeWhyWhat to do
The output does nothing when the input triggersThe join, not the halves.Print the value and the decision. You will see which is wrong inside a minute.
It triggers constantlyThe threshold is on the wrong side.Swap > for <, or move the number.
It worked, now it does notAlmost always a wire pulled loose.Check the wires you moved most recently, not the code you changed.
It flickers on the boundaryChatter.Trigger above one number, release below a lower one.

Before you leave

  • Ten out of ten.
  • Your observation list and three fixes.
  • A label on the machine, and the code saved.
  • Everything packed against the bin card.
Challenge optional — only if you finish early
  • Give somebody your machine with the label covered up. Watch what they do.
29. The input half